The present invention relates to tetraamido macrocyclic ligands that form complexes with transition metals, and more particularly to the synthesis of a novel diamidiol that is used as a substrate in an improved synthesis of macrocycles such as exemplified by 5,6-Benzo-3,8,11,13-tetraoxo-2,2,9,9-tetramethyl-12,12-diethyl-1,4,7,10-tetraazacyclotridecane, H4.
The use of transition metal chelates as catalysts for bleaching agents is well known in the art. For example, U.S. Pat. No. 4,119,557, issued to Postlethwaite, discloses the use of iron-polycarboxyamine complexes with hydrogen peroxide releasing substances to clean fabrics. Similarly, U.S. Pat. No. 5,244,594 (Favre et al.), U.S. Pat. No. 5,246,621 (Favre et al.), U.S. Pat. No. 5,194,416 (Jureller et al.), and U.S. Pat. No. 5,314,635 (Hage et al.) describe the use of manganese complexes of nitrogen- (or other heteroatom-) coordinated macrocycles as catalysts for peroxy compounds.
The utility of compounds of this type has motivated researchers to develop new ligands that both stabilize the catalyst complex and that are able to withstand an oxidative environment. Promising ligands in this respect are the tetraamido macrocycles represented by structure 10 shown in FIG. 1 which, when complexed with a transition metal such as iron, afford particularly good dye transfer inhibition capabilities.
An azide-based synthesis of the macrocycle is described by Collins et al. in J. Am. Chem. Soc., vol. 113, No. 22, page 8419 (1991). A problem with this synthesis is that it produces the tetraamido macrocycle in yields of only about 12% (starting from 1,2-phenylenediamine, as shown in the scheme at page 8422 of the article) and employs isolation techniques which cannot be adapted to large scale production. (Note: The identical synthesis is described by Erich S. Uffelman in his Ph.D. dissertation at California Institute of Technology (1992) and is the work upon which the synthesis of the journal article is based.)
Another synthetic route to the macrocycle is described in U.S. Pat. No. 5,853,428, issued also to the same Collins, and employs a ring forming strategy that is the reverse of the earlier published synthesis. In this synthesis, xcex1-aminoisobutyric acid is used as a starting material to form the intermediate diacid 18 shown in FIG. 1, which is then coupled with an aryl diamine to yield the macrocycle (as shown in the scheme at col. 15 of the patent). This later synthesis, described by Collins as now being his preferred synthesis, provides the macrocycle structure in two steps and in an improved overall yield of about 18% (starting from diethyl malonyl dichloride). (Note: The identical synthesis is described by Scott W. Gordon-Wylie in his Ph.D. dissertation at Carnegie Mellon University (1995) and is the work upon which the synthesis of the patent is based.)
However, a number of problems exist with the Collins patent synthesis. For one, xcex1-aminoisobutyric acid is a relatively expensive starting material. Further, the yield of the diacid is only about 50-60% from that starting material and usually requires further purification. Additionally, the first step, a double coupling, is said to require 72-144 hours for completion, while the second step, a ring closure, requires 48-110 hours. Still further, the use of large amounts of anhydrous pyridine as solvent are apparently required in both steps, which is commercially prohibitive. For commercial purposes, a more efficient and less expensive synthesis of the tetraamido macrocycle is required than is provided by either of the two prior art syntheses just described.
Briefly, the present invention comprises an improved synthesis of tetraamido-macrocyclic ligands as exemplified by 5,6-benzo-3,8,11,13-tetraoxo-2,2,9,9-tetramethyl-12,12-diethyl-1,4,7,10-tetraazacyclotridecane, H4. In the improved synthesis, a previously unreported diamidodiol is formed in high yield from diethylmalonyl dichloride and the relatively inexpensive starting material 2-amino-2-methyl-1-propanol. The novel diamidodiol is then oxidized to the diacid used in the synthesis of the Collins patent described above. Coupling of the diacid with an aryl diamine then yields the macrocycle according to the procedure found in the same patent. However, in the improved synthesis of the present invention, not only is a less expensive starting material used but the yield of the diacid is increased from the 50-60 % obtained in the prior art to approximately 74%. Additionally, the improved synthesis avoids the use of anhydrous pyridine solvent, which is also expensive. Further, the present invention produces an easily isolable product (i.e., the diacid) in excellent purity, whereas in the Collins patent the synthesis involves a tedious work-up procedure and produces a product that typically requires recrystallization. The present invention requires that the intermediate diacid be made in two steps, but these steps are considerably more viable from a commercial standpoint than the Collins synthesis, both in terms of simplicity of performance and cost.